Abstract:

A device, in particular, for inductively heating up a heating element by
means of an inductor and an element for recording a reference quantity
which is dependent on the temperature of the heating element and derived
from the electric quantity of the inductor in such a way that it makes it
possible to form the reference value from the reference quantity and to
adjust the temperature according to the reference quantity adjustment by
means of the reference value. The aim of said invention is to carry out a
reliable adjustment of a water temperature or of a cooked product even at
extreme conditions or when the reference value is incorrect. For this
purpose, the device comprises a correction means for correcting the
reference value.

Claims:

1-13. (canceled)

14. A device for heating up a heating element, in particular with an
inductor, a radiant element or a gas burner, and comprising means for
recording a reference variable dependent upon a temperature of the
heating element, means for forming a reference value from the reference
variable and for controlling the temperature on the basis of controlling
the reference variable with the aid of the reference value, and
correcting means for correcting the reference value for control of the
heating element temperature.

15. The device as claimed in claim 14, wherein the correcting means has an
inputting means for input of a correcting command by an operator for the
purpose of correcting the reference value.

16. The device as claimed in claim 14, wherein the correcting means is
prepared for the control operation purpose of altering the reference
value by a correction value in response to a correction command.

17. The device as claimed in claim 14, wherein the correcting means is
prepared for the purpose of automatically correcting the reference value
at a temperature control start point, in particular for altering the
reference value by a correction value.

18. The device as claimed in claim 16, wherein the correction value is a
preset value.

19. The device as claimed in claim 16, wherein the correction value is
dependent upon the reference variable.

20. The device as claimed in claim 16, wherein the correction value is
dependent upon a heating parameter determined prior to the control
operation.

21. The device as claimed in claim 16, wherein the correction value is
dependent upon a determined characteristic of a cooked product to be
heated up.

22. The device as claimed in claim 14, wherein the correcting means is
prepared for the purpose of correcting the reference variable following a
start signal for initiating the temperature control and for forming the
reference value from the corrected reference variable.

23. The device as claimed in claim 22, wherein the correction comprises a
reduction of the heat output for the heating element to an intermediate
value.

24. The device as claimed in claim 23, wherein the intermediate value is a
value already established prior to the start signal.

25. The device as claimed in claim 23, wherein the intermediate value
substantially corresponds to the output required to maintain a desired
temperature of the heating element.

26. The device as claimed in claim 14, wherein the reference variable is
derived from an electrical variable of an inductor.

27. A cooking appliance comprising:a heating element heated by a heating
means selected from the group consisting of an inductor, a radiant
element, or a gas burner;means for recording a reference variable, the
reference variable being dependent upon a temperature of the heating
element;means for forming a reference value from the reference variable
and for controlling the heating element temperature on the basis of
controlling the reference variable with the aid of the reference value;
andcorrecting means for correcting the reference value, wherein the
reference value may be corrected by a correction value in response to an
outside manual input command or by an automatic correction value.

28. The device as claimed in claim 27, wherein the correction value is a
preset value.

29. The device as claimed in claim 27, wherein the correction value is
dependent upon the reference variable, a heating parameter determined
prior to the control operation, or a determined characteristic of a
cooked product to be heated up.

30. The device as claimed in claim 27, wherein the correcting means
corrects the reference variable following a start signal for initiating
the temperature control and forms a new reference value from the
corrected reference variable.

31. The device as claimed in claim 30, wherein the correction comprises a
reduction of the heat output for the heating element to an intermediate
value.

32. The device as claimed in claim 31, wherein the intermediate value is a
value already established prior to the start signal.

33. The device as claimed in claim 31, wherein the intermediate value
substantially corresponds to the output required to maintain a desired
temperature of the heating element.

Description:

[0001]The invention relates to a device, in particular for inductively
heating up a heating element according to the preamble of claim 1.

[0002]WO 2004/103028 A1 discloses a temperature controller for an
induction furnace, in which an operator can start the control operation
at a desired point in time by input of a corresponding command. A control
unit records a value of a controlled variable associated with the
temperature of a cooking vessel at this start time and controls the
output of the inductor in such a way that the controlled variable remains
as close as possible to this reference value. The controlled value of the
temperature controller is derived from an electrical variable of the
inductor of the induction furnace. For example, if water in the cooking
vessel readily begins to boil following heating up of the cooking vessel,
the operator can allow the water to continue to simmer as desired by
initiating the control process.

[0003]The object of the present invention is to provide a device of the
type in question with which the temperature of a heating element, or the
temperature of a cooked product at the heating element, may be controlled
more reliably. This object is achieved according to the invention by the
features of claim 1. Advantageous embodiments and developments of the
invention may be found in the subclaims.

[0004]The invention is based on a device for heating up a heating element
in particular with an inductor, a radiant element or a gas burner, and on
a means for recording a reference variable dependent upon a temperature
of the heating element and derived from an electrical variable of the
inductor for the purpose of forming a reference value from the reference
variable and controlling the temperature on the basis of control of the
reference variable with the aid of the reference value. It is proposed
that the device comprises a correcting means for correcting the reference
value. The reference value may be corrected manually by an operator or
automatically, or adjusted to new requirements in such a way that uniform
retention of a desired temperature may be achieved by simple means. A
reference variable dependent upon the temperature of the heating element,
which variable is derived from an electrical variable of the inductor,
conventionally correlates with the temperature of a merely very thin
layer of the heating element, for example of a pan base, which layer
faces towards the inductor. The temperature of this very thin layer does
not necessarily correspond to the temperature of, for example, cooked
product or water in the pan. In the case where the pan is rapidly heated
up by a supplied large heat output, the pan base for example, in
particular the lowermost layer of the pan base, is already substantially
hotter than the boiling point of water when the water first begins to
boil. If the automatic temperature control is initiated by an operator at
this time, and if the reference value is formed from the reference
variable and the reference variable is kept as close as possible to the
reference value, it may be that the pan base remains held at a very hot
temperature, the initially simmering water begins to boil briskly, and an
operator would like to reduce the supplied heat output. With the use of
the correcting means, the reference value may be corrected and the
reference variable adjusted with the aid of the new reference value, in
particular to match the new reference value. This applies correspondingly
to devices in which the temperature of a wall of the heating element is
cooled with an infrared sensor in a known way, or in which a temperature
sensor is arranged beneath a plate for deposition of the heating element.
In this arrangement the device has e.g. a radiant element or a gas
burner.

[0005]Depending on the selection of electrical variable or electrical
variables of the inductor, from which variable or variables the reference
variable is derived, the reference variable may also depend upon the
output of the inductor. If the output is changed suddenly, for example by
initiation of the temperature control by an operator, the reference
variable may fluctuate greatly and the temperature control may take place
in an unreliable and undesirable manner. In this case also, reliable
temperature control may be simply achieved by correcting the reference
value, for example after the heating system has settled into its steady
state. A corresponding situation applies in the case of devices with
radiant elements or gas burners.

[0006]Recording of the reference variable may take place by measuring
and/or calculating. The reference value used may be the value of the
reference variable at a specific point in time, for example the starting
time. The means for recording the reference variable may comprise the
correcting means. It is also possible for a control unit, for example a
microcontroller, to contain both the means for recording the reference
variable and the correcting means. The correcting means may be a matching
means for matching the reference value to a new state or a new condition.
The reference variable may be used as a controlled variable. It is
purposefully adjusted to the reference value. The reference value may be
constant over time or be a function of time.

[0007]In an advantageous embodiment of the invention, the correcting means
has an inputting means for input of a correction command by an operator
for the purpose of correcting the reference value. The reference value
and therewith the temperature control may be adjusted by simple means
manually and reliably to the requirements of the operator.

[0008]The correcting means is purposefully prepared for the purpose of
altering the reference value by a correcting value in response to a
correction command. The reference value is hereby corrected in discrete
steps, as a result of which the correction per se, retracing of the
correction and handling by an operator are kept simple.

[0009]In a further embodiment of the invention, the correcting means is
prepared for the purpose of automatically correcting the reference value
at the start of the temperature control, in particular for altering it by
a correction value. This correction is especially advantageous in the
case of systematic errors induced for example by a dependence of the
reference variable on the output of the inductor. The reference value may
be calculated at the start of the temperature control and subsequently
corrected. It is also possible for the reference value to be determined
at the start of the temperature control on the basis of an already
corrected calculation or from the corrected reference variable, without
said reference value being previously determined uncorrected. The start
of the temperature control may occur automatically or in response to an
operator command.

[0010]An especially simple correction occurs when the correction value is
a preset value. The correction value may be an absolute value or a
relative value which depends, for example, on the magnitude of the
reference variable. In the case of dependence of the correction value on
the reference variable--as a preset or non-preset value--an especially
operator-friendly correction can be achieved, since multiple corrections
can be avoided. In the case of a high temperature of the heating element,
the correction value may, for example, be greater than in the case of a
low temperature. Moreover, in the case of a high output of the inductor
at the start of the temperature control, a higher correction value may be
selected than if the output were lower.

[0011]The correction value is advantageously dependent upon a heating
parameter determined prior to the control, for example the heat output,
the temperature of the heating element, or for example a temperature
gradient of the heating element. By this means corrections may be made
very rapidly and multiple corrections may be avoided. Rapid and effective
correction may similarly be achieved by the correction value being
dependent upon a determined characteristic of a cooked product to be
heated up. For example, if there is a lot of water--in what follows also
considered to be a cooked product--in the pan to be heated up, a large
correction value may be selected, and if there is little water a small
one may be selected.

[0012]It is also proposed that the correction means is prepared for the
purpose of correcting the reference variable following a signal start at
the beginning of the temperature control and of forming the reference
value from the corrected reference variable. By this means, the device
may be brought from an extreme situation, for example the use of a
maximal output, prior to a determination of the reference value, and
brought into the state which it has during the temperature control. The
reference value may be formed from a reference variable which is
determined in a state that is at least similar to the state during the
temperature control, and a systematic error in the determination of the
reference value can be corrected and a reliable temperature control
achieved.

[0013]The state of the device may be brought from an extreme state
especially simply, if the correction comprises e.g. a reduction in the
output of the inductor to an intermediate value. Intermediate value is to
be understood as an output value which, from a chronological point of
view, is positioned downstream of the start signal and upstream of the
control phase.

[0014]The intermediate value is advantageously a value already established
prior to the start signal, by means of which a very simple correction is
achieved. An especially effective correction may be achieved when the
intermediate value substantially corresponds to the output required to
maintain a desired temperature of the heating element, in particular the
temperature exhibited by the heating element at the time of the start
signal. As a result of this, the state of the device at the time of
determination of the reference value is similar to the state assumed by
said device during the control operation, with the result that a
dependence of the reference variable on, for example, the output of the
inductor can be substantially abolished as a trigger of a systematic
error.

[0015]Further advantages will emerge from the following description of the
drawings. The drawings represent exemplary embodiments of the invention.
The drawings, the description and claims contain numerous features in
combination. The person skilled in the art will expediently also consider
the features individually, and combine them into advantageous further
combinations.

[0016]The drawings are as follows:

[0017]FIG. 1: A device for inductively heating up a heating element in a
schematic view;

[0018]FIG. 2: A diagram on which a reference variable for a temperature
controller, the output of the inductor, and the water and pan temperature
are plotted against time;

[0019]FIG. 3: The diagram as in FIG. 2 with a larger quantity of water in
the pan;

[0020]FIG. 4: The diagram from FIG. 2 with a systematic error in the
reference variable, and

[0021]FIG. 5: The diagram from FIG. 4, in which the systematic error has
been eliminated.

[0022]FIG. 1 shows a device 2 for inductively heating up a heating element
4 in the form of a pan base of a pan 6. For the purpose of heating, the
pan 6 stands on a base plate 8 under which an inductor 10 is arranged.
Connected to the inductor 10, there is a control unit 12 comprising a
means 14 for recording a reference variable dependent upon the
temperature of the heating element 4 and derived from an electrical
variable of the inductor 10. The device 2 also has a correcting means 16,
comprising parts of the control unit 12 and an inputting means 18 for
input of the correction command by an operator. The inputting means 18
has two keys 20 with which a reference value formed by the control unit
12--and therewith a target temperature of the heating element 4--may be
corrected in an upward or downward direction. Alternatively, a
radiant-heat carrier or a gas burner may also be provided as the heat
source. The means 14 may be formed on a temperature sensor arranged above
or below the base plate 8. The measured temperature forms the reference
variable F; it may deviate more or less markedly from the actual
temperature T of the pan 6.

[0023]FIG. 2 shows a diagram in which the temperature TH of the
heating element 4 during inductive eating is plotted against time t. The
temperature TW of water simultaneously heated in the pan 6 by
heating up of the heating element 4 is also plotted against time t. The
temperature TW here gives the temperature TW of the lowermost
layer of water in the pan 6, which layer is adjacent to the heating
element 4. Water layers lying thereabove are somewhat colder whilst the
water is being heated up. In FIG. 2, the heat output P of the inductor 10
is plotted against time t using a thick continuous line. A reference
variable F is additionally plotted against time t, said variable F being
determined by the means 14 from the inductivity of the system with the
inductor 10 and the heating element 4, and in particular from the current
flow through the inductor 10.

[0024]At the start of a heating-up process at time t0, both the
heating element 4 and the water lying thereabove are at, for example,
room temperature. For heating up of the heating element 4 and of the
water, the heat output P is switched to a relatively high level, the
heating element 4 is heated up and therewith--somewhat delayed in
time--the water above the heating element 4. With the increase in
temperature TH, the inductivity of the system comprising the heating
element 4 decreases and therewith also the reference variable F.

[0025]At time t1 the water has reached the temperature T1, which
an operator would like to maintain. For example, the water has begun to
boil gently. By simultaneously pressing the two keys 20, the operator
generates a start signal for initiating a temperature control. During
this temperature control, the reference variable F, and therewith the
temperature TH of the heating element 4, are maintained at a
constant level in order also to maintain the water thereabove at a
constant temperature level. At time t1, the heating element 4 has,
in its lowermost layer which is most relevant for recording of the
reference variable, the temperature T2, which may be, for example,
115° C. and therefore not inconsiderably above the temperature
T1 of the water, 100° C. If the heating element 4 were now to
remain constantly at the temperature T2 of 115° C., the
heating element 4 would, as during the heating up process, continue to
give off heat to the water, and the water would be heated more strongly
and ultimately boil briskly.

[0026]In order to prevent this, the control process is initiated as
follows: the reference variable F has, at time t1, decreased by a
very large amount and has reached a reference value F1, which may be
recorded by the means 14 or derived from the reference variable F. In
response to the start signal, the reference value F1 is raised by
the correcting means 16 by a preset correction value FK1, to a new
reference value F2. The reference variable F is now adjusted to the
new reference value F2, by markedly reducing the heat output P of
the inductor 10. As a result of this, the heating element 4 cools from
the temperature T2 of 115° C. to temperature T3, for
example, 107° C. The water temperature TW still fluctuates
somewhat above the temperature T1, since a certain quantity of heat
of high temperature TH is still stored in the heating element 4 and
given off to the water. However, by mixing of the water layers in the pan
6, the lower layer of the water now cools slowly and falls for example
below the temperature T1, which the operator had specified as a
desired temperature, the water stops boiling and is perceived as being
too cold by the operator. By operating the key 20 with the "+", the
latter triggers a correction of the reference value F2 by a new,
preset correction value FK2, to a new reference value F3. By
this means the temperature TH of the heating element 4 is set to a
somewhat higher temperature T4, by which the water is heated up
somewhat, reaches the desired temperature T1 and for example again
simmers lightly.

[0027]FIG. 3 shows the control process as represented in FIG. 2, the pan 6
containing, however--as distinct from FIG. 2--a considerably greater
quantity of water. With equal heat output P of the inductor 10 following
an initiation of heating, not shown in FIG. 3, the temperature TH of
the heating element 4, and therewith the temperature TW of the
water, rises substantially more slowly than in FIG. 2. This lesser
temperature gradient of the heating element 4 is recorded by the control
unit 12. At the start signal at time t1, the reference value F1
is corrected by a correction value FK3 to the new reference value
F2, which is selected to be greater than the correction value
FK1 from FIG. 2 since, from the heat output P in association with
the small temperature gradient of the heating element 4, a large water
volume has been concluded and the correction value FK3 has been set
in dependence on the volume of water. In FIG. 3, as in FIG. 2, the
temperature TW of the water falls below the desired temperature
T1 due to mixing of the water, and the operator corrects the
temperature TH accordingly at time t2 by operating the key 20
with the "+". By this correction, the reference value F2 is
corrected via a correction value FK4 to a new reference value
F3, the correction value FK4 being greater than the correction
value FK2 in FIG. 2 due to the large volume of water. In another
process, the correction values FK3 and FK4 are dependent upon
the reference variable F and are selected by an operator to have, for
example, a high value when a high temperature T1 is selected and a
low value when a low temperature T1 is selected.

[0028]FIG. 4 shows a further process performed by the device for
inductively heating up the heating element 4, which is the same as the
process in FIG. 2 as far as time t1, when the operator
simultaneously presses the keys 20 and triggers the start signal. As
described in FIG. 2, the heat output P of the inductor 10 is strongly
reduced following giving of the start signal, in order to end the process
of heating up the water. Depending on the nature of derivation of the
reference variable from one or more electrical variables of the inductor
10, the systematic error of the reference variable F depending on the
heat output P of the inductor 10 may arise. In FIG. 4 a dependence of the
reference variable F on the heat output P is shown, in which the
reference variable F also falls when there is a fall in the heat output
P. If the reference value F1 is now determined directly after the
start signal and still before downward regulation of the heat output P,
the means 14 or the control unit 12 will upwardly regulate the reference
variable F, which has decreased from the reference value F1 to a
value F4 due to the fall in the heat output P, to the reference
value F1, as shown in FIG. 4. This is associated with a decrease in
the temperature TH of the heating element 4 from the temperature
T2 to the temperature T3, as a result of which the water cools
markedly and rapidly falls below the desired temperature T1. This
systematic error may be eliminated manually by a manual correction at
time t2.

[0029]FIG. 5 shows a process by which the systematic error shown in FIG. 4
is counteracted. The reference value F1 is not formed immediately
after the start signal, but the heat output P is first of all lowered to
an intermediate value PZ and held there briefly until time t2.
Due to the systematic error, the reference variable F falls to the value
F4 and rises slightly until time t2, due to cooling of the
heating element 4 from the temperature T2 to the temperature
T3. During this time the whole system may pass from the heating-up
state prior to time t1 and settle into a less dynamic state in which
the reference value F3 is not formed until time t2 and the
reference variable F is adjusted to this reference value F3. By this
means the water which, following a brief period of further heating up due
to residual warmth in the heating element 4 and cooling by mixing in the
pan 6, has now become too cool, is again brought to the desired
temperature T1.

[0030]The intermediate value PZ is selected in such a way that it
substantially corresponds to the output required for maintenance of a
desired temperature T1, as shown in FIG. 5. Alternatively, it is possible
to set the intermediate value PZ to a value already established
prior to the start signal, as a result of which the control is especially
simple.